take a look at the attached photo (it's photoshoped but it's exactly what I see in my phone), what could cause this ? it's not just that the colors levels also seem to change automatically while moving the camera and sometimes it gets so dark at the edges.

I have Fcam installed, and I am pretty sure that the lens is clean.

EDIT :
the upper picture is what the camera sees (the problem)
the bottom picture is what the camera should see